Modern wireless communication is based on generating and receiving electromagnetic (EM) waves that span a wide frequency range, from Hz to THz, providing abundant band resources. However, there are draw-backs to EM communication, including high extinction coefficient for electrically conductive materials and antenna size. On the other hand, animals have effectively used acoustic waves for short-range communication for millions of years. Acoustic wave based communication can overcome some of the EM difficulties.
For example, acoustic waves propagate well in conductive materials, and have thus been explored for underwater communication by submarines. Marine mammals such as whales and dolphins are known to communicate effectively via acoustic waves. In land-based acoustic wave communication, the audible band or acoustic band (i.e., about 20 Hz to 20 kHz, sounds that are capable of being heard by humans) is often occupied by human conversations, while the subsonic band can be disturbed by moving vehicles and building construction.
The ultrasonic band, while having a wide frequency span and often free of disturbance, is rarely exploited for high data rate communication purposes. The ultrasonic band is frequencies that are greater than the upper limit of the human hearing range, and is generally taken to be greater than about 20 kHz. One important reason that the ultrasonic band is rarely used is the lack of wide bandwidth ultrasonic generators and receivers. Conventional piezoelectric-based transducers only operate at one resonance frequency, preventing use in communications where wider bandwidth is needed for embedding information streams.